Health care for older Americans with chronic conditions is often fragmented and provider-centric. In response, a team of investigators at Johns Hopkins University has translated the scientific principles of 7 successful innovations in chronic care into 1 patient-centered delivery system. Supported by evidence-based guidelines and state-of-the-art information technology, "Guided Care" is now undergoing a 12-month pilot test on older primary care patients with complex needs. A specially trained Guided Care Nurse (GCN), based in a primary care practice, collaborates with 2 primary care physicians to provide 7 services for 40-60 high-risk patients: comprehensive assessment and care planning, prompting "best practices" for chronic conditions, promoting self-management, encouraging healthy life styles, coordinating care, educating and supporting unpaid caregivers, and accessing community resources. The multi-site study we propose will measure the effects of Guided Care on the quality and outcomes of care for high-risk older persons, their unpaid caregivers, and their primary care physicians. The panels of 22 physicians in 6 practices will be screened to identify 1350 high-risk older patients. After 850 have given informed consent and baseline interviews, clusters of 1-3 physicians at each practice site will be randomized to provide either Guided Care or usual care to their consenting patients. Each physician cluster assigned to the Guided Care group will incorporate a GCN into its practice; the physician clusters assigned to the control group will continue providing "usual care" without GCNs. Interviews and queries of administrative databases will provide evaluative data at baseline and at 12-and 24-month follow-up intervals. The primary outcome variable is the participants' physical and mental health (SF-36 Physical Health and Mental Health Summary Scales). Secondary outcome variables include: participants' quality of care; unpaid caregivers' burden, costs, health, and satisfaction; and primary care physicians' satisfaction with chronic care. Intention-to-treat analyses will have 85% power (range 70-97 percent) to detect clinically meaningful differences between the 2 groups' physical and mental health. The study is designed to facilitate the prompt dissemination of Guided Care, if the results of the trial are favorable. A Stakeholders' Advisory Board, representing U.S. consumers, providers, delivery systems, insurers, regulators and policy-makers, will inform the operation and evaluation of the study-and it will facilitate the subsequent dissemination of Guided Care tools and technology throughout American health care.